Rock Formations Around Aoshima (“Ogre’s Washboard”)

The wave-cut rock formations extending along 8 kilometers of Miyazaki coastline around Aoshima are known locally as the 'ogre's washboard' for the ridged pattern visible from a distance. They formed over millions of years as alternating layers of harder sandstone and softer mudstone, laid down underwater between 2 and 24 million years ago, tilted upward by tectonic activity, then worn unevenly by the sea. The mudstone eroded faster, leaving the sandstone ridges standing proud. The formations around Aoshima are designated a Natural Monument of Japan and stretch south past Tosakibana Cape toward Kinchakujima island.